The polypropylene resin is excellent in rigidity, hardness and heat resistance and can be easily molded into desired shape by any of various techniques such as injection molding, calendering and extrusion. Further, the polypropylene resin is cheap. Therefore, the polypropylene resin is widely used in automotive interior parts (automotive inner trims) such as an instrumental panel, a trim and a pillar, and automotive exterior parts (automotive outer trims) such as a fender, a bumper, a side moul, a mud guard and a mirror cover.
In the application of the polypropylene resin to the above uses, it is common practice to prepare, in accordance with the intended use, polypropylene resin compositions with desired properties by compounding polypropylene resin with a high-pressure polyethylene, a soft polymer or rubber component such as polyisobutylene, polybutadiene and ethylene/propylene copolymer (EPR), an inorganic filler, etc.
Specifically, it is known to utilize, for example, a reinforced polypropylene resin composition comprising polypropylene (crystalline ethylene/propylene block copolymer) and an inorganic filler in which an ethylene/.alpha.-olefin copolymer rubber is contained as a soft polymer or rubber component (Japanese Patent Laid-open Publication No. 59(1983)-168649) and compositions containing hydrogenated block copolymer rubbers and/or ethylene/propylene copolymer rubbers (Japanese Patent Laid-open Publication Nos. 3(1991)-172339, 61(1986)-12742, 61(1986)-291247, 63(1988)-150343 and 4(1992)-57848).
It is required that the above polypropylene resin compositions have further enhanced properties. For example, in the use in automotive inner trims, improvements of the rigidity, impact resistance and heat resistance of the polypropylene resin compositions are demanded for realizing the reduction of the thickness and weight of the inner trims. Molding composed of the polypropylene resin compositions can be brought to practical use in unpainted form if flow marks and weld are not noticeable and if the polypropylene resin compositions are excellent in appearance and scratch resistance.
For example, as a polypropylene resin composition having improved rigidity, heat resistance (thermal deformation resistance), impact resistance and appearance, a polypropylene resin composition comprising a crystalline polypropylene, a hydrogenated block copolymer with a high styrene component content, a hydrogenated block copolymer with a high conjugated diene (hydrogenated) unit content and talc was proposed in Japanese Patent Laid-open Publication No. 8(1996)-20684. However, it is demanded that the composition described in this publication be improved in impact resistance and molding appearance.
The inventors have conducted extensive and intensive studies with a view toward obtaining a polypropylene resin composition satisfying the above performance requirements. As a result, it has been found that a polypropylene resin composition obtained from a crystalline polypropylene, a product of hydrogenation of aromatic vinyl/conjugated diene block copolymer and an inorganic filler having an average particle size as small as 0.1 to 3 .mu.m optionally together with an aromatic hydrocarbon copolymer, a crystalline polyethylene and a soft ethylene/.alpha.-olefin copolymer is excellent in rigidity and heat resistance and is endowed with high impact resistance and appearance enhancing effect. The present invention has been completed on the basis of this finding.